System and Method for Locating Individuals and Equipment, Airline Reservation System, Communication System

ABSTRACT

A system for locating an individual in a facility, the system comprising a portable wireless transponder device borne by the individual; an interrogator; and a plurality of antennas distributed in the facility, the antennas being selectively separately connected to the interrogator, the interrogator when connected to any of the antennas having a communications range covering less than the area of the entire facility, the interrogator being configured to repeatedly transmit a wireless command to the portable wireless transponder device using alternating antennas, the portable wireless transponder device being configured to transmit data identifying the portable wireless transponder device in response to a command if the portable wireless transponder device is within communications range of the antenna sending the command, the individual being locatable by determining with which antenna the interrogator was able to establish communications with the portable wireless transponder device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 11/271,935,filed Nov. 10, 2005, titled “System and Method for Locating Individualsand Equipment, Airline Reservation System, Communication System”, whichis a continuation of U.S. patent application Ser. No. 10/326,762, filedDec. 20, 2002, now U.S. Pat. No. 7,030,732, issued Apr. 18, 2006, whichin turn is a continuation of U.S. patent application Ser. No.09/628,876, filed Jul. 26, 2000, now U.S. Pat. No. 6,509,829, issuedJan. 21, 2003, which in turn is a continuation of U.S. patentapplication Ser. No. 09/305,182, filed May 3, 1999, now U.S. Pat. No.6,127,917, issued Oct. 3, 2000, which in turn is a continuation of U.S.patent application Ser. No. 08/807,678, filed Feb. 27, 1997, now U.S.Pat. No. 5,914,671, issued Jun. 22, 1999, all of which are incorporatedherein by reference.

TECHNICAL FIELD

The invention relates to personnel locating systems, travel reservationsystems, airport security systems, radio frequency identificationdevices.

BACKGROUND OF THE INVENTION

Travel reservation and baggage tracking systems are known in the art.Passengers typically purchase tickets in advance of travel, and areincluded in a database of a reservation system as having a reservation.On the date of travel, they must check in, or their seat will be givenup to other passengers. Because statistics show that there will alwaysbe a number of passengers who will not show up on the designated date oftravel, carriers typically “overbook” by selling a number of seats overthe number of seats that are actually available, based on mathematicalcalculations. If the passenger does not check in, their seat may be usedto accommodate overbooking, or may be given to standby passengers. Thefollowing U.S. patents relate to reservation systems and areincorporated herein by reference: U.S. Pat. Nos. 5,401,944; 5,151,692;5,051,565; 5,010,240; 4,984,156; 4,931,932; 4,449,186; 4,247,795;3,750,103.

When a passenger enters a travel depot (e.g., an airport), they musttherefore check in to make sure the carrier (e.g., airline) knows theyare present and to make sure that their seat is not given away tosomeone else. This typically involves standing in line and waiting foran employee to verify that the correct traveler is bearing a ticket. Theemployee receives the ticket and, using a reservation system, issues aboarding pass, with a seat assignment, indicating to the system that theseat is no longer available to be given away.

Traditionally, check in occurred simultaneously with a baggage check-in,with an employee marking the traveler's luggage with a tag indicting thedestination where the bag is to be sent, printing a baggage receipt forthe customer, and logging the bag in the reservation and baggagehandling system.

Business travelers, however, typically do not have any bags to check andprefer not to wait in line. Also, many airports offer curbside check-in,which allows a passenger to check in bags at the curb before enteringthe airport, where lines are shorter because a gratuity is expected. Thebusiness travelers and travelers who have used the curbside check intypically go directly to the podium adjacent the departure gate andcheck in there. While the line at the podium may be shorter, it is stilla line. Travelers needing to check in baggage must wait in lines.

There are many reasons why it would be useful to determine the presenceof an individual in an airport or other travel depot. If a flight isabout to leave, airline staff may desire to make an attempt to determineif a checked in passenger is in the airport. It is also frequentlydesirable to locate airline staff, such as pilots, flight attendants,wheelchair attendants, mechanics etc., or airport staff, such assecurity, or merchants or other persons who work in airports, for avariety of reasons. This is presently attempted through paging, which issometimes difficult to hear, and is often annoying or competing withmore important messages, such as gate change announcements, orinformation about which rows are boarding.

It is also useful to determine the location of a passenger in evaluatingterrorist threats. A terrorist who has planted a bomb in his or herluggage is likely to leave the premises and not board the flight forwhich the luggage was checked.

Passengers in airports typically need gate and flight information in ahurry. Such information may be obtained from airline staff, but thistypically involves standing in long lines. This information is thereforemore typically gathered by reading a monitor which lists flight numbers,destinations, gates, and status. A problem is that in some airports,each airline has their own monitors, so a traveler may have to walk agreat distance to try to find a monitor for a particular airline.Monitors also contain vast amounts of information, most of it of nointerest to a particular traveler. This makes it difficult to finduseful information in a hurry.

Switching antennas connected to an interrogator is disclosed in commonlyassigned U.S. patent application Ser. No. 08/772,173, filed Dec. 18,1996, titled “Communication System Including Diversity Antenna Queuing,”and listing Clifton W. Wood, Jr. as inventor, now U.S. Pat. No.5,842,118. Antenna switching for this application is performed fordiversity purposes.

SUMMARY OF THE INVENTION

The invention provides a system for locating an individual in afacility. The system comprises a portable wireless transponder deviceborne by the individual; an interrogator; and a plurality of antennasdistributed in the facility. The antennas are selectively separatelyconnected to the interrogator. The interrogator, when connected to anyof the antennas has a communications range covering less than the areaof the entire facility. The interrogator repeatedly transmits a wirelesscommand to the portable wireless transponder device using alternatingantennas. The portable wireless transponder device transmits dataidentifying the portable wireless transponder device in response to acommand if the portable wireless transponder device is withincommunications range of the antenna sending the command. Thus, theindividual is located by determining with which antenna the interrogatorwas able to establish communications with the portable wirelesstransponder device.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a plan view of a travel depot facility, such as an airport,including a system, embodying the invention, for locating an individual.

FIG. 2 is a block diagram of the system of FIG. 1, further including aninterface with an airline reservation and baggage tracking system, andfurther including monitors for displaying information of particularinterest to passengers in the area of the monitor.

FIG. 3 is a perspective view showing a monitor included in the system ofFIG. 2.

FIG. 4 is a front view of a card used in the system of FIG. 1 or 2.

FIG. 5 is a circuit schematic of an interrogator included in the systemof FIG. 1 or 2.

FIG. 6 is a circuit schematic of circuitry included in card of FIG. 4.

FIG. 7 is a block diagram of an interrogator included in the system ofFIG. 1 or 2.

FIG. 8 is a circuit schematic of DPSK circuitry included in theinterrogator of FIG. 7.

FIG. 9 is a circuit schematic of RF circuitry included in theinterrogator of FIG. 7.

FIG. 10 is a plan view of a card in accordance with an alternativeembodiment of the invention.

FIG. 11 is a block diagram illustrating assembly of the card of FIG. 10.

FIG. 12 is a flow chart illustrating a routine run by the system of FIG.1 or 2 to log locations of individuals.

FIG. 13 is a flow chart illustrating a routine run by the system of FIG.1 or 2, used in connection with the routine of FIG. 12, to determine thelocation of an individual.

FIG. 14 is a flow chart illustrating a routine run by the system of FIG.2 to check in a passenger using the card of FIG. 4 or 10 as anelectronic boarding pass.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws “to promote the progressof science and useful arts” (Article 1, Section 8).

FIG. 1 shows a travel depot facility 10, such as an airport, including asystem 12 (see FIG. 2) for locating an individual. The facility 10includes various areas of a typical facility such as a main terminalarea 14 which typically includes a baggage check in area 16, shops,restaurants, etc. The facility 10 further includes a terminal concoursearea 18 which one enters after passing a security check point 20. Theterminal concourse area 18 includes multiple gate doors 22 definingcontrolled access points. More particularly, the gate doors 22 aretypically locked until a flight is available for departure or is beingdeplaned. Airline staff control passage through the gate doors and onlypermit people with boarding passes through the gate doors 22. The gatedoors 22 lead to jetways 24 which are movable to define a path into anairplane. The terminal area 18 typically includes podiums 28 whereairline personnel are located. The terminal area 18 also includesmultiple seating areas 30 which may be grouped off by gate.

The system 12 (see FIG. 2) includes portable wireless transponderdevices 32 borne by passengers, airport employees, contractors, airlineand contractor employees, etc. In the illustrated embodiment, thedevices 32 include circuitry such as the circuitry described in detailin commonly assigned U.S. patent application Ser. No. 08/705,043, filedAug. 29, 1996, now U.S. Pat. No. 6,130,602, and incorporated herein byreference. In one embodiment, the portable transponder devices 32 havecard shaped housings with length and width dimensions corresponding tostandard length and width dimensions of credit cards. In one embodiment,the transponder devices 32 include photographs of the respectiveindividuals associated with the devices. The transponder devices 32 are,more particularly, intelligent radio frequency identification devices orremote intelligent communications (RIC) devices which communicate atmicrowave frequencies.

FIG. 4 shows but one example of a housing for a device 32, in the formof an employee identification badge or card including an intelligentradio frequency identification device integrated circuit 34. Theintegrated circuit 34 includes a transmitter, a receiver, amicroprocessor, and a memory. The housing for the device 32 shown inFIG. 4 includes a card 36 made of plastic or other suitable material. Inone embodiment, the integrated circuit 34 is laminated to the back faceof the card 36, and the card forms a visible portion of the badge. Inanother embodiment, the integrated circuit 34 is bonded to the back faceof the card by embedding it within a thin bond line of epoxy-basedmaterial. Alternatively, the integrated circuit 34 is embedded into theplastic card 36. In one embodiment, the front face of the badge hasvisual identification features including a photograph 38 of the beareras well as identifying text. The device 32 further includes asend/receive antenna 40 coupled to the integrated circuit 34, and abattery 42 coupled to the integrated circuit 34 to supply power to theintegrated circuit. The battery 42 and antenna 40 are embedded orsupported inside the plastic card 36.

The battery 42 can take any suitable form. Preferably, the battery typewill be selected depending on weight, size, and life requirements for aparticular application. In one embodiment, the battery 42 is a thinprofile button-type cell forming a small, thin energy cell more commonlyutilized in watches and small electronic devices requiring a thinprofile. A button-type cell has a pair of electrodes, an anode formed byone face and a cathode formed by an opposite face. Exemplary button-typecells are disclosed in several pending U.S. patent applicationsincluding U.S. patent application Ser. No. 08/205,957, “Button-TypeBattery Having Bendable Construction and Angled Button-Type Battery,”listing Mark E. Tuttle and Peter M. Blonsky as inventors, now U.S. Pat.No. 5,432,027; U.S. patent application Ser. No. 08/321,251, “Button-TypeBatteries and Method of Forming Button-Type Batteries,” listing Mark E.Tuttle as inventor, now U.S. Pat. No. 5,494,495; and U.S. patentapplication Ser. No. 08/348,543, “Method of Forming Button-TypeBatteries and a Button-Type Battery Insulating and Sealing Gasket,”listing Mark E. Tuttle as inventor. These patent applications andresulting patents are hereby incorporated by reference. In analternative embodiment, the battery 42 comprises a series connected pairof button type cells. Alternative power supplies can be used instead ofbatteries, in alternative embodiments.

FIG. 5 illustrates but one alternative housing supporting the circuit34. More particularly, FIG. 5 illustrates a miniature housing 42encasing the circuit 34 to define a tag which can be supported by aperson or object. The housing 42 preferably has the general shape andsize, in plan view, of a postage stamp. The embodiment of FIG. 5 alsohouses a card 44 supporting the circuit 34 in the housing 42. The card44 is formed of plastic or other suitable material having a thickness ofabout 0.040 inches, a width of about 1.25 inches, and a height of about1.25 inches. In one embodiment, the circuit 34 is bonded to a back faceof the card 44 with a thin layer of non-conductive epoxy material thatcooperates with the card to define the housing 42. The circuit 34 iscoupled to a send antenna 48, and a receive antenna 46, and receivespower from a battery 42 which can be similar to the battery included inthe embodiment of FIG. 4. The battery 42, and antennas 46 and 48 aresupported in the housing 42 by the card 44.

Although two particular types of housings have been disclosed, thecircuit 34 can be included in any appropriate housing. The circuit 34 isof a small size that lends itself to applications employing smallhousings, such as cards, miniature tags, etc. Larger housings can alsobe employed. The circuit 34, housed in any appropriate housing, can besupported from a person, or attached to a object (or a peoplespossessions) in any desired manner; for example using double sided tape,glue, lanyards, leash, nails, staples, rivets, or any other fastener.The housing can be sewn on to an object, hung from an object, implantedin an object (hidden), etc.

Various configurations are possible for the antenna connected to thecircuit 34. In one embodiment, separate antennas 46 and 48 are providedfor receiving and sending (FIG. 5). In another embodiment, a singleantenna 40 is shared by the receiver and transmitter (FIG. 4). In oneembodiment, one or more antennas are defined by conductive epoxyscreened onto a card or housing. In the illustrated embodiment, theantenna is conductively bonded to the integrated circuit 34 via bondingpads.

The system 12 further includes an interrogator 50. The card 36 transmitsand receives radio frequency communications to and from the interrogator50. The system 12 further includes an array of antennas 52 (orsend/receive antenna pairs) alternately coupled to the interrogator 50.The interrogator 50 includes transmitting and receiving circuitry,similar to that implemented in the circuit 34. In one embodiment, thesystem 12 further includes a controller 54. In the illustratedembodiment, the controller 54 is a computer. The controller 54 acts as amaster in a master-slave relationship with the interrogator 50. Thecontroller 54 includes an applications program for controlling theinterrogator 50 and interpreting responses, and a library of radiofrequency identification device applications or functions. Most of thefunctions communicate with the interrogator 50. These functions effectradio frequency communication between the interrogator 50 and the card32. In one embodiment, the controller 54 and the interrogator 50 arecombined together (e.g., in a common housing), or functions of the hostcomputer are implemented in hard wired digital logic circuitry.

In the illustrated embodiment, the communications system 10 includesmultiple selectable transmit antennas X1, X2, X3 etc., and multiplereceive antennas R1, R2, R3 etc. connected to the interrogator 50. Eachantenna pair X1, R1, X2, R2, etc. defines an antenna 52 of the antennaarray for purposes of the discussion below. In one embodiment, thecommunications system 10 includes combined antennas that are used bothfor transmitting and receiving by the interrogator 50. Generally, theinterrogator 50 transmits an interrogation signal or command, such as an“Identify” command, (“forward link”) via one of the antennas 52. Thecard 32 receives the incoming interrogation signal via its antenna, ifit is within receiving range of the particular antenna 52 used totransmit. Upon receiving the signal, the card 32 responds by generatingand transmitting a responsive signal or reply (“return link”). Theinterrogator 50 is described in greater detail below.

In the illustrated embodiment, the responsive signal is encoded withinformation that uniquely identifies, or labels the particular card 32that is transmitting, so as to identify any object or person with whichthe card 32 is associated.

In the embodiment illustrated in FIG. 2, multiple cards 32 are employed;however, there is no communication between the cards 32. Instead, themultiple cards 32 communicate with the interrogator 50. Multiple cards32 can be used in the same range of an antenna 52.

Various U.S. patent applications, which are incorporated herein byreference, disclose features that are employed in various alternativeembodiments of the invention: Ser. No. 08/092,147, filed Jul. 15, 1993,“Wake Up Device for a Communications System” and continuationapplication Ser. No. 08/424,827, filed Apr. 19, 1995, “Wake Up Devicefor a Communications System”; Ser. No. 08/281,384, filed Jul. 27, 1994,“Communication System Having Transmitter Frequency Control”; Ser. No.07/990,918, filed Dec. 15, 1992, now U.S. Pat. No. 5,365,551, “DataCommunication Transceiver Using Identification Protocol”; Ser. No.07/899,777, filed Jun. 17, 1992, “Radio Frequency Identification Device(RFID) and Method of Manufacture, Including an Electrical OperatingSystem and Method,” now abandoned; Ser. No. 07/151,599, filed Nov. 12,1993, now U.S. Pat. No. 5,406,263, “Anti-Theft Method for Detecting TheUnauthorized Opening of Containers and Baggage,”; Ser. No. 07/168,909,filed Dec. 17, 1993, now U.S. Pat. No. 5,497,140, “Electrically PoweredPostage Stamp or Mailing or Shipping Label Operative with RadioFrequency (RF) Communication,”; and Ser. No. 08/032,384, filed on Mar.17, 1993, “Modulated Spread Spectrum in RF Identification SystemsMethod,” now allowed.

The integrated circuit 34 is advantageous over prior art devices thatutilize magnetic field effect systems because, with the circuit 34, agreater range can be achieved, and more information can be obtained(instead of just an identification number). As a result, the circuit 34can be used for the application of the present invention, wheretransmission over a large range is required. In one embodiment, thesensitivity of the cards 32 is adjustable so that only devices within anadjustable range of an antenna 52 will respond. In another embodiment,the power of the interrogator 50 is adjustable so that only deviceswithin a certain range of an antenna 52 will respond.

A power conservation problem is posed by such implementations wherebatteries are used to supply power to the integrated circuits 34. If theintegrated circuit 34 operates continuously at full power, battery lifewill be short, and card 32 will have to be frequently replaced. If thebattery 42 is permanently sealed in a housing, replacement of thebattery will be difficult or impossible. For example, one reason forsealing the battery with the integrated circuit 34 and antenna(s) in ahousing is to simplify the design and construction, to reduce the costof production, and protect the electrical interconnections betweendevices. Another reason is protection of the battery and integratedcircuit 34 from moisture and contaminants. A third reason is to enhancethe cosmetic appeal of the card 32 by eliminating the need for an accessport or door otherwise necessary to insert and remove the battery. Whenthe battery is discharged, the entire badge or stamp is then discarded.It is therefore desirable to incorporate power conservation techniquesinto the integrated circuit 32 in order to extend useful life.

FIG. 6 is a circuit schematic of the integrated circuit 34 utilized inthe devices of FIG. 4 or 5. In the embodiment shown in FIG. 6, thecircuit 34 is a monolithic integrated circuit. In the illustratedembodiment, the integrated circuit 34 comprises a single die, having asize of 209×116 mils². The integrated circuit 34 includes a receiver 56,a transmitter 58, a micro controller or microprocessor 60, a wake uptimer and logic circuit 62, a clock recovery and data recovery circuit64, and a bias voltage and current generator 66.

In one embodiment, the circuit 34 switches between a “sleep” mode ofoperation, and higher power modes to conserve energy and extend batterylife during periods of time where no interrogation signal is received bythe circuit 34. The wake up timer and logic circuitry 62 provides thisswitching.

In one embodiment, a spread spectrum processing circuit 68 is alsoincluded in the circuit 34. In this embodiment, signals transmitted andreceived by the interrogator 50, and signals transmitted and received bythe circuit 34 are modulated spread spectrum signals. Spread spectrummodulation is described below. In one illustrated embodiment, themodulation scheme for replies sent by the transmitter 58 is selectable.One of the available selections for replies sent by the transmitter 58is modulated spread spectrum.

Spread Spectrum Modulation

Many modulation techniques minimize required transmission bandwidth.However, the spread spectrum modulation technique employed in theillustrated embodiment requires a transmission bandwidth that is up toseveral orders of magnitude greater than the minimum required signalbandwidth. Although spread spectrum modulation techniques are bandwidthinefficient in single user applications, they are advantageous wherethere are multiple users, as is the case with the instant circuit 34.The spread spectrum modulation technique of the illustrated embodimentis advantageous because the interrogator signal can be distinguishedfrom other signals (e.g., radar, microwave ovens, etc.) operating at thesame frequency. The spread spectrum signals transmitted by the circuit34 and by the interrogator 50 are pseudo random and have noise-likeproperties when compared with the digital command or reply. Thespreading waveform is controlled by a pseudo-noise or pseudo randomnumber (PN) sequence or code. The PN code is a binary sequence thatappears random but can be reproduced in a predetermined manner by thecircuit 34. More particularly, incoming spread spectrum signals aredemodulated by the circuit 34 or by the interrogator 50 through crosscorrelation with a version of the pseudo random carrier that isgenerated by the circuit 34 itself or the interrogator 50 itself,respectfully. Cross correlation with the correct PN sequence unspreadsthe spread spectrum signal and restores the modulated message in thesame narrow band as the original data.

A pseudo-noise or pseudo random sequence (PN sequence) is a binarysequence with an autocorrelation that resembles, over a period, theautocorrelation of a random binary sequence. The autocorrelation of apseudo-noise sequence also roughly resembles the autocorrelation ofband-limited white noise. A pseudo-noise sequence has manycharacteristics that are similar to those of random binary sequences.For example, a pseudo-noise sequence has a nearly equal number of zerosand ones, very low correlation between shifted versions of the sequence,and very low cross correlation between any two sequences. A pseudo-noisesequence is usually generated using sequential logic circuits. Forexample, a pseudo-noise sequence can be generated using a feedback shiftregister.

A feedback shift register comprises consecutive stages of two statememory devices, and feedback logic. Binary sequences are shifted throughthe shift registers in response to clock pulses, and the output of thevarious stages are logically combined and fed back as the input to thefirst stage. The initial contents of the memory stages and the feedbacklogic circuit determine the successive contents of the memory.

The illustrated embodiment employs direct sequence spread spectrummodulation. A direct sequence spread spectrum (DSSS) system spreads thebaseband data by directly multiplying the baseband data pulses with apseudo-noise sequence that is produced by a pseudo-noise generator. Asingle pulse or symbol of the PN waveform is called a “chip.”Synchronized data symbols, which may be information bits or binarychannel code symbols, are added in modulo-2 fashion to the chips beforebeing modulated. The receiver performs demodulation. For example, in oneembodiment the data is phase modulated, and the receiver performscoherent or differentially coherent phase-shift keying (PSK)demodulation. In another embodiment, the data is amplitude modulated.Assuming that code synchronization has been achieved at the receiver,the received signal passes through a wideband filter and is multipliedby a local replica of the PN code sequence. This multiplication yieldsthe unspread signal.

A pseudo-noise sequence is usually an odd number of chips long. In theillustrated embodiment, one bit of data is represented by a thirty-onechip sequence. A zero bit of data is represented by inverting thepseudo-noise sequence.

Spread spectrum techniques are also disclosed in the following patentapplications and patent, which are incorporated herein by reference:U.S. patent application Ser. No. 08/092,147; U.S. patent applicationSer. No. 08/424,827, filed Apr. 19, 1995, now U.S. Pat. No. 5,790,946;and U.S. Pat. No. 5,121,407 to Partyka et al. They are also disclosed,for example, in “Spread Spectrum Systems,” by R. C. Dixon, published byJohn Wiley and Sons, Inc.

Backscatter and Frequency Hopping

The interrogator 50 sends out a command that is spread around a certaincenter frequency (e.g., 2.44 GHz). After the interrogator transmits thecommand, and is expecting a response, the interrogator switches to a CWmode (continuous wave mode). In the continuous wave mode, theinterrogator does not transmit any information. Instead, theinterrogator just transmits 2.44 GHz radiation. In other words, thesignal transmitted by the interrogator is not modulated. After thecircuit 34 receives the command from the interrogator, the circuit 34processes the command. If the circuit 34 is in a backscatter mode italternately reflects or does not reflect the signal from theinterrogator to send its reply. For example, in the illustratedembodiment, two halves of a dipole antenna are either shorted togetheror isolated from each other to send a reply.

Frequency hopping is employed in one embodiment. In the illustratedembodiment, frequency hopping does not occur when the interrogatortransmits a command, but occurs when the interrogator is in thecontinuous wave mode. The interrogator, in the continuous wave mode,hops between various frequencies close to the 2.44 GHz frequency. Thesevarious frequencies are sufficiently close to the 2.44 GHz frequencythat backscatter antenna reflection characteristics of the circuit 34are not appreciably altered. Because the interrogator is hopping betweenfrequencies, the interrogator knows what frequency backscatterreflections to expect back from the circuit 34. By hopping betweenvarious frequencies, the amount of time the interrogator continuouslyuses a single frequency is reduced. This is advantageous in view of FCCregulatory requirements.

In one illustrated embodiment, no attempt is made to frequency hop atthe interrogator to a pseudo-random sequence and then correlate to thatat the receiver. However, in alternative embodiments, such correlationtakes place.

In one embodiment, the transmitter 58 is switchable between operating ina modulated backscatter transmitter mode, and operating in an activemode. The transmitter 58 switches between the backscatter mode and theactive mode in response to a radio frequency command, instructing thetransmitter to switch, sent by the interrogator 50 and received by thereceiver 56. In the active mode, a carrier for the transmitter 58 isextracted from a signal received by the receiver 56.

Active transmitters are known in the art. See, for example, U.S. patentapplication Ser. No. 08/281,384; U.S. patent application Ser. No.08/281,384 also discloses how transmit frequency for the transmitter 58is recovered from a message received via radio frequency from theinterrogator 50.

In one embodiment, the transmitter 58 is capable of transmitting usingdifferent modulation schemes, and the modulation scheme is selectable bythe interrogator. More particularly, if it is desired to change themodulation scheme, the interrogator sends an appropriate command viaradio frequency. In this embodiment, the transmitter can switch betweenmultiple available modulation schemes such as Binary Phase Shift Keying(BPSK), Direct Sequence Spread Spectrum, On-Off Keying (OOK), andModulated Backscatter (MBS).

In one embodiment, the clock for the entire integrated circuit 16 isextracted from the incoming message itself by clock recovery and datarecovery circuitry 64. This clock is recovered from the incomingmessage, and used for timing for the micro controller 60 and all theother clock circuitry on the chip, and also for deriving the transmittercarrier or the subcarrier, depending on whether the transmitter isoperating in active mode or backscatter mode.

In addition to recovering a clock, the clock recovery and data recoverycircuit 64 also performs data recovery on valid incoming signals. Thevalid spread spectrum incoming signal is passed through the spreadspectrum processing circuit 68, and the spread spectrum processingcircuit 68 extracts the actual ones and zeros of data from the incomingsignal. More particularly, the spread spectrum processing circuit 68takes the chips from the spread spectrum signal, and reduces eachthirty-one chip section down to a bit of one or zero, which is passed tothe micro controller 60.

The micro controller 60 includes a serial processor, or I/O facilitythat received the bits from the spread spectrum processing circuit 68.The micro controller 60 performs further error correction. Moreparticularly, a modified hamming code is employed, where each eight bitsof data is accompanied by five check bits used by the micro controller60 for error correction. The micro controller 60 further includes amemory, and after performing the data correction, the micro controller60 stores bytes of the data bits in memory. These bytes contain acommand sent by the interrogator 50. The micro controller 60 responds tothe command.

For example, the interrogator 50 may send a command over one of theantennas 52 requesting that any integrated circuit 34 in communicationsrange of that antenna 52 respond with the integrated circuit'sidentification number. Status information is also returned to theinterrogator 50 from the integrated circuit 34 when the circuit 34responds.

The transmitted replies have a format similar to the format of incomingmessages. More particularly, a reply starts with a preamble (e.g., allzeros in active mode, or alternating double zeros and double ones inbackscatter mode), followed by a Barker or start code which is thirteenbits long, followed by actual data.

No stop bits are included in the incoming message or reply, in thepreferred embodiment. Instead, part of the incoming message describeshow many bytes are included, so the integrated circuit 34 knows how muchinformation is included. Similarly, part of the outgoing reply describeshow many bytes are included, so the interrogator 50 knows how muchinformation is included. The incoming message and outgoing replypreferably also include a check sum or redundancy code so that theintegrated circuit 34 or the interrogator 50 can confirm receipt of theentire message or reply.

After the reply is sent, the integrated circuit 34 returns to the sleepmode, and the wake up timer and logic circuit 62 starts timing again forthe next wake up (e.g., in 16 milliseconds, or whatever period isselected).

The interrogator 50 provides a communication link between the controller54 and the integrated circuit 34. In one embodiment, the interrogator 50connects to the controller 54 via an IEEE-1284 enhanced parallel port(EPP). The interrogator communicates with the circuit 34 via a selectedRF (microwave) antenna 52.

In one embodiment, communications from the interrogator 50 to thecircuit 34, and communications from the circuit 34 to the interrogator50 use different physical protocols.

The physical communications protocol for communications from theinterrogator 50 to the circuit 34 is referred to as the “forward link”protocol. The forward link data is sent in the following order:

Preamble

Barker Code

Command Packet

Check Sum

A Maximal Length Pseudo Noise (PN) Sequence is used in the DirectSequence Spread Spectrum (DSSS) communications scheme in the forwardlink. In one embodiment, the sequence is generated by a linear feedbackshift register of the form [5,2]. That is, there are five registers, theoutput of the second register is X-ORed with the output of the fifthregister, and the result is fed into the input of the first registerone. This produces a repeating 31 “chip” sequence. The sequence endswith all registers set to one. The sequence is taken from the output ofthe first register. This code is synchronous with the data in that eachdata bit comprises one and only one full PN sequence. The chip sequencefor each bit is:

001 1010 0100 0010 1011 1011 0001 1111.

Other embodiments are, of course, possible. For example, other forms oflinear feedback shift registers can be employed.

In one embodiment, a zero bit is transmitted as one inverted full cycleof the PN sequence. A one bit is transmitted as one full non-invertedcycle of the PN sequence.

In the illustrated embodiment, the data is not differentially encoded.

In one embodiment, there are at least two available “chipping” rates.One rate is 9.5375 Mchips/sec (high band) and another rate is 4.768750Mchips/sec (low band).

The preamble precedes the data. In one embodiment, the preamble includesa series of zeros, followed by a start or Barker code. In embodimentswhere the transponder 16 includes wake up timer and logic circuitry 36,the preamble includes a series of zeros for a duration equal to thewakeup interval (e.g., 5, 16, 64, or 256 ms) plus 2 milliseconds,followed by a start or Barker code.

In one embodiment, the Barker code is defined by the following bitstring:

1111 1001 1010 1. Other embodiments are possible.

Command data is grouped into 13-bit words. Each word includes eight databits (D7, D6, D5, D4, D3, D2, D1, D0) and five ECC (Error CorrectionCode) bits (P4, P3, P2, P1, and P0). In one embodiment, the bittransmission order is (with D7 transmitted first):

D7, D6, D5, D4, D3, D2, D1, D0, P4, P3, P2, P1, P0 . . .

In one embodiment, the ECC bits (P4-P0) are generated using thefollowing equations:P0=(D1+D2+D5+D7)modulo 2P1=[(D1+D3+D4+D6)modulo 2]ComplementP2=(D0+D2+D3+D6+D7)modulo 2P3=[(D0+D4+D5+D6+D7)modulo 2]ComplementP4=(D0+D1+D2+D3+D4+D5)modulo 2.

Data rates depend on which data band is being used. A high data band hasan effective data rate (adjusting for PN and ECC) of 189.3 Kbps. A lowdata band has an effective data rate of 94.68 Kbps.

In the illustrated embodiment, a 16-bit check sum is provided to detectbit errors on the packet level. A circuit 34 can be programmed to eitherreturn a reply if a bad check sum is found in the forward link, or tosimply halt execution and send no replies. In one embodiment, a 16 bitCRC is employed in the forward link, the return link, or both, insteadof or in addition to the check sum.

The physical communications protocol for communications from the circuit34 to the interrogator 50 is referred to as the “return link” protocol.In the illustrated embodiment, the return link messages are sent in thefollowing order:

Preamble

Barker Code

Reply Packet

Check Sum

After sending a command, the interrogator sends a continuous unmodulatedRF signal with a frequency of 2.44175; Ghz. Return link data isDifferential Phase Shift Key (DPSK) modulated onto a square wavesubcarrier with a frequency of 596.1 Khz. A data 0 corresponds to onephase and data 1 corresponds to another, shifted 180 degrees from thefirst phase. The subcarrier is used to modulate antenna impedance of acard 32. For a simple dipole, a switch between the two halves of thedipole antenna is opened and closed. When the switch is closed, theantenna becomes the electrical equivalent of a single half-wavelengthantenna that reflects a portion of the power being transmitted by theinterrogator. When the switch is open, the antenna becomes theelectrical equivalent of two quarter-wavelength antennas that reflectvery little of the power transmitted by the interrogator. The switchdriving a printed half wavelength dipole antenna gives a typical rangeof 15 feet when the interrogator 50 transmits at 30 dBm into a 6 dB gainantenna. Therefore, antennas 52 are located no more than 15 feet apartin areas of the facility 10 where it is desirable to locate people orobjects.

The preamble for the return link includes 2000 bits, alternating 2 zerosthen 2 ones, etc., and a 13-bit start (Barker) code. Alternativepreambles are possible.

In the illustrated embodiment, the start code or Barker Code is definedby the following bit string: 1111 1001 1010 1.

The reply link data is grouped in 13 bit words. Each word is composed of8 data bits (D7, D6, D5, D4, D3, D2, D1, D0) and 5 ECC bits (P4, P3, P2,P1, P0).

The Block Encoded Sequence is D7, D6, D5, D4, D3, D2, D1, D0, P4, P3,P2, P1, P0.

The Block ECC Bits (P4-P0) are generated using the following equations:P0=(D1+D2+D5+D7)modulo 2P1=[(D1+D3+D4+D6)modulo 2]ComplementP2=(D0+D2+D3+D6+D7)modulo 2P3=[(D0+D4+D5+D6+D7)modulo 2]ComplementP4=(D0+D1+D2+D3+D4+D5)modulo 2.

In the illustrated embodiment, the bit duration is 6.71 μs making theeffective data rate 91.75 Kbps for the return link.

In the illustrated embodiment, a 16-bit check sum is provided to detectbit errors on the packet level. In one embodiment, a 16 bit CRC isemployed in addition to or instead of the check sum.

Each pair of data words is interleaved, starting with the Barker codeand the first data word. The transmitted bit order for two sequentialwords, A and B, is D7A, D7B, D6A, D6B, D5A, D5B, D4A, D4B, D3A, D3B,D2A, D2B, D1A, D1B, D0A, D0B, P4A, P4B, P3A, P3B, P2A, P2B, P1A, P1B,P0A, P0B.

D7A is the first transmitted bit. In the illustrated embodiment, DPSK isapplied to the interleaved data.

In one embodiment (see FIG. 7), the interrogator 50 includes enhancedparallel port (EPP) circuitry 70, DPSK (differential phase shift keyed)circuitry 72, and RF (radio frequency) circuitry 74, as well as a powersupply (not shown) and a housing or chassis (not shown). In theillustrated embodiment, the enhanced parallel port circuitry 70, theDPSK circuitry 72, and the RF circuitry 74 respectively define circuitcard assemblies (CCAs). The interrogator uses an IEEE-1284 compatibleport in EPP mode to communicate with the controller 54. The EPPcircuitry 70 provides all the digital logic required to coordinatesending and receiving a message to and from a circuit 34. The EPPcircuitry 70 buffers data to transmit from the controller 54, convertsthe data to serial data, and encodes it. The EPP circuitry 70 then waitsfor data from the circuit 34, converts it to parallel data, andtransfers it to the controller 54. In one embodiment, messages includeup to 64 bytes of data.

The EPP mode interface provides an asynchronous, interlocked, byte wide,bidirectional channel controlled by the controller 54. The EPP modeallows the controller 54 to transfer, at high speed, a data byte to/fromthe interrogator within a single host computer CPU I/O cycle (typically0.5 microseconds per byte).

The DPSK circuitry 72 (see FIG. 8) receives signals I and Q from the RFcircuitry 74 (described below), which signals contain the DPSK modulatedsub-carrier. The DPSK circuitry 72 includes anti-aliasing filters 76 and78 filtering the I and Q signals, respectively, and analog to digital(A/D) converters 80 and 82 respectively coupled to the filters 76 and 78and respectively converting the filtered signals from analog to digitalsignals. The DPSK circuitry 72 further includes a combiner 84, coupledto the A/D converters 80 and 82, combining the digital signals. The DPSKcircuitry 72 further includes a FIR matched filter 86, coupled to thecombiner 84, which filters the combined signals. The DPSK circuitry 72further includes delay circuitry 88 and multiplier circuitry 90 coupledto the FIR matched filter 86 for delaying the signal and multiplying thesignal with the delayed signal to remove the sub-carrier. The DPSKcircuitry 72 further includes low pass filter circuitry 92, coupled tothe multiplier 90, filtering the output of the multiplier 90 to removethe X2 component. The DPSK circuitry 72 further includes a bitsynchronizer 94 coupled to the filter 92 for regeneration of the dataclock. The DPSK circuitry 72 further includes lock detect circuitry 96coupled to the low pass filter 92 and generating a lock detect signal.The data, clock, and lock detect signal are sent to the EPP circuitry70.

The RF circuitry 74 (see FIG. 9) interfaces with the transmit andreceive antennas X1, X2, X3, etc., and R1, R2, R3, etc defining antennas52. The RF circuitry modulates the data for transmission to a circuit34, provides a continuous wave (CW) carrier for backscattercommunications with a circuit 34 (if backscatter communications areemployed), and receives and downconverts the signal received from thetransponder unit (which is a backscatter signal in one embodiment).

The RF circuitry 74 also includes a power divider 98, and a frequencysynthesizer 100 coupled to the power divider 98. The frequencysynthesizer 100 tunes the RF continuous waver carrier for frequencyhopping and band selection. The RF circuitry defines a transmitter, andreceives data from the EPP circuitry 70. The RF circuitry 74 includes anamplitude modulation (AM) switch 102 that receives the data from the EPPcircuitry 70 and amplitude modulates the data onto a carrier. Moreparticularly, the AM switch 102 turns the RF on and off (ON OFF KEY).The RF circuitry 74 further includes a power amplifier 104, coupled tothe AM switch 102, to amplify the signal. The RF circuitry 74 furtherincludes a switch 106, coupled to the power amplifier 104, fortransmission of the amplified signal through a selected one of thetransmit antennas X1, X2, X3, etc.

During continuous wave (CW) transmission for the backscatter mode, theAM switch 102 is left in a closed position. When the interrogator 50 istransmitting in the CW mode, the circuit 34 backscatters the signal witha DPSK modulated sub carrier. This signal is received via one of thereceive antennas R1, R2, R3, etc. More particularly, the RF circuitry 74further includes a switch 108 coupled to the receive antennas R1, R2,R3, etc. In another alternative embodiment, such as when backscattercommunications are not employed, the RF circuitry uses common antennasfor both transmission and reception, and alternates use of antennas frommultiple available send/receive antennas. The RF circuitry 74 furtherincludes a low noise amplifier (LNA) 110 coupled to the switch 108 andamplifying the received signal. The RF circuitry 74 further includes aquadrature downconverter 112, coupled to the LNA 110, coherentlydownconverting the received signal. The RF circuitry 74 further includesautomatic gain controls (AGCs) 114 and 116 coupled to the quadraturedown converter 112. The amplitude of the signals are set using theautomatic gain controls 114 and 116 to provide the signals I and Q. TheI and Q signals, which contain the DPSK modulated sub-carrier, arepassed on to the DPSK circuitry 72 (FIG. 8) for demodulation.

Although one interrogator 50 has been described, it may be desirable toprovide multiple interrogators depending on the size and layout of afacility, in which case the multiple interrogators will preferably shareinformation.

The interrogator or interrogators 50 are respectively selectivelyconnected to the antennas 52 of an array of antennas distributed in atleast the passenger areas of the facility, such as in the main terminal14, the baggage check in area 16, the terminal concourse area 18, andthe security check area 20. An interrogator connected to any of theantennas 52 has a range covering less than the area of the entirefacility 10. More particularly, the more antennas 52 that are provided,the more precisely the location of an individual can be determined (thetransmission and reception range of the interrogator can be decreasedappropriately). Preferably, some antennas 52 are located innon-passenger areas, such as outdoor areas, to assist in locatingindividuals or equipment instead of passengers. The antennas 52 aredesigned for transmission and reception at microwave frequencies (e.g.,2.44 GHz). As described above, the antennas 52 can either comprisecombined send/receive antennas, or separate antennas for sending(transmitting) and receiving. If separate antennas are used for sendingand receiving, they will be referred to as a single antenna for purposesof the following discussion and claims.

Preferably, the antennas 52 are distributed fairly evenly throughoutmonitored areas of the facility 10. In one embodiment, an area ofcommunication is defined by the interrogator 50 connected to an antenna52, and the area of communication of the interrogator using one of theantennas 52 overlaps with the area of communication of the interrogatorusing another one of the antennas 52 so that there are no gaps in theareas of the facility desired to be covered by the system.

In operation, the interrogator 52 repeatedly transmits a wirelesscommand to the portable wireless transponder device using alternatingones of the antennas 52. In one embodiment, the interrogator issequentially connected to respective antennas 52, and makes at least onecommunication attempt using each antenna 52. The device 32 owned by anindividual or supported by an object or checked or carry-on luggagetransmits data identifying the device 32 (and thus the bearer orpossessor of the device 32) in response to an interrogator command ifthe device 32 is within communications range of the antenna 52 sendingthe command. Thus, the individual or object is located by determiningwith which antenna the interrogator 50 was able to establishcommunications with the portable wireless transponder device.

FIGS. 12 and 13 illustrate routines executed by the controller 54 tolocate individuals, equipment, or checked or carry-on baggage in thefacility 10. Note that it may be useful for an airline to determine thelocation of checked baggage, using the system of the invention, forvarious reasons. For example, it may be useful to locate a piece ofbaggage that has been misplaced, or that is destined for a flight thatis about to leave, or a piece of baggage that is in transit to a plane,but must be re-routed to a different plane. It may be useful to locate apiece of carry on baggage using the system of the invention for variousreasons. For example, if a piece of carry on baggage becomes separatedfrom its owner for a predetermined time, an assumption can be made thatit is either lost or else creates a possible bomb risk that should beinvestigated. Also, the system can be used to locate a passenger's lostcarry on or checked baggage.

The routine of FIG. 12 is continuously run (during hours of operation ofthe facility) and includes a step 118 of causing the interrogator tosend an “identify” command, which requests that all devices 32 (withincommunication range) reply with their respective identification numbers.After performing step 118, the controller 54 proceeds to step 120.

In step 120, the controller 54 deletes old entries and logsidentification numbers of devices 32 within the range of the antenna 52being used. After performing step 120, the controller 54 proceeds tostep 122.

In step 122, the controller switches the antenna 52 (or antenna pair)being used by the interrogator. After performing step 122, thecontroller 54 proceeds to step 118.

The routine of FIG. 13 is run when it is desired to locate a specificindividual, item of equipment, piece of carry-on baggage, or piece ofchecked baggage (by inputting an identification number of a device 32).

The routine of FIG. 13 includes a step 124 of receiving (inputting) aninquiry as to the location of a particular individual. After performingstep 124, the controller 54 proceeds to step 126.

In step 126, the controller determines if the individual (or item ofequipment, or piece of carry-on baggage, or piece of checked baggage) ison the carrier (plane) by checking the logs for antennas at controlledaccess points (e.g., the gate for the flight the individual wasscheduled to take). After performing step 126, the system proceeds tostep 128.

In step 128, a determination is made as to whether the individual (oritem of equipment, or piece of carry-on baggage, or piece of checkedbaggage) is on the carrier. If so, the controller proceeds to step 130.If not, the controller proceeds to step 132.

In step 130, the location of the individual (or item of equipment, orpiece of carry-on baggage, or piece of checked baggage) is displayed asbeing on board the carrier (e.g. the airplane). After performing step130, execution terminates.

In steps 132 and 134 (which can be combined), current (most recent) logsare read for all other antennas, and the controller searches for theparticular individual (or item of equipment, or piece of carry-onbaggage, or piece of checked baggage) in these logs. After performingsteps 132 and 134, the controller proceeds to step 136.

In step 136, a determination is made as to whether the particularindividual (or item of equipment, or piece of carry-on baggage, or pieceof checked baggage) was located in any of these logs. If so, thecontroller proceeds to step 140. If not, the controller proceeds to step138.

In step 138, the controller causes a display to be generated that thesearch failed or the individual (or item of equipment, or piece ofcarry-on baggage, or piece of checked baggage) was not located on thepremises. After performing step 138, execution terminates.

In step 140, a determination is made as to whether the individual (oritem of equipment, or piece of carry-on baggage, or piece of checkedbaggage) was located in more than one log in logs associated with morethan one antenna). If so, the controller proceeds to step 142. If not,the controller proceeds to step 144.

In step 142, the location is displayed of the antenna where the loggedcommunication with the device of the particular individual (or item ofequipment, or piece of carry-on baggage, or piece of checked baggage)took place. This is presumably where the individual (or item ofequipment, or piece of carry-on baggage, or piece of checked baggage) ispresently located. After performing step 142, execution terminates.

In step 144, because the individual has been logged in more than oneantenna location, all antenna locations can be displayed or, in theillustrated embodiment, triangulation or telemetry are used, and/orrelative signal strengths measured by the multiple antennas for the lastlogged reply by the card are used, to locate with particularity theparticular individual's location (or the location of the item ofequipment, or piece of carry-on baggage, or piece of checked baggage).Optionally, the direction of travel is also determined by determiningchange in triangulated location with respect to time. After performingstep 144, the controller proceeds to step 146.

In step 146 the controller causes the location of the particularindividual (or item of equipment, or piece of carry-on baggage, or pieceof checked baggage) to be displayed. After performing step 146, thecontroller proceeds to step 148.

This system and routine can be used to track the location of equipmentbearing the circuit 34, carry-on baggage bearing the equipment, orchecked baggage bearing the equipment.

In one embodiment of the invention, the system 12 further comprises acarrier (e.g., airline) reservation and baggage tracking system 152(FIG. 2). Any presently used reservation system can be employed. Forexample, a system such as the systems described in incorporated U.S.Pat. Nos. 5,401,944; 5,151,692; 5,051,565; 5,010,240; 4,984,156;4,931,932; 4,449,186; 4,247,795; and 3,750,103 can be employed for thecarrier reservation and baggage tracking system 152. The reservation andbaggage tracking system 152 includes a computer having a databasestoring information identifying passengers who have purchased ticketsfor passage (e.g., a flight), information about scheduled departures(e.g., for flights), information identifying passengers who have checkedin (e.g., for a flight), etc. The system 12 further includes a network154 connecting the interrogator 50 to the carrier reservation andbaggage tracking system 152. Any appropriate network, such as a localarea network, wide area network, Intranet network, Internet network,etc. can be employed. If multiple airlines or carriers in the facilityhave separate reservation systems, the network 154 preferably connectsall participating reservation systems to the interrogator 50.

In this embodiment, the card 32 is used to automatically check in apassenger who enters the facility or a designated area of the facility(e.g., a gate area), as desired.

More particularly, the interrogator 50 defines a wireless transponder incommunication with the computer of the carrier reservation and baggagetracking system 152. The interrogator periodically sends wirelesscommands requesting responses from portable identification devices(e.g., the cards 32). The cards 32 transmitting identifying data (e.g.,a serial number that is associated with the bearer, a Social SecurityNumber, a frequent flyer number, a confirmation number, etc.) inresponse to receiving a command from the interrogator. The interrogatorhas a desired coverage area (e.g., in the airport, or in the gate area),and communicates only with cards 32 within the desired area. Thecomputer of the carrier reservation and baggage tracking system 152modifies the reservation database to indicate that a passenger haschecked in, in response to the interrogator 50 receiving a response froma card 32 in the desired coverage area. Thus, the card 32 acts as anelectronic boarding pass, saving the passenger from having to stand inline to check in, and reducing labor required by the carrier.

Conditions can be imposed before the electronic boarding pass isaccepted. For example, in one embodiment, the electronic boarding pass(card 32) is accepted to check in a passenger only within apredetermined time period before a scheduled departure. Thus, if apassenger is in the airport the day before a flight (e.g., to greet anarriving passenger, or for an unrelated flight), the passenger is notconsidered to be checked in. In one embodiment, the electronic boardingpass is only accepted if the response from the card 32 includesidentifying data for a passenger for whom the database in the carrierreservation and baggage tracking system 152 indicates that a ticket fora flight has been purchased. A routine for execution by the system 152to this effect is provided in FIG. 14, and includes a first step 156 inwhich the system 152 retrieves a list of passengers having reservationsfor flights scheduled to leave in the next predetermined time period(e.g., flights scheduled to leave in the next two hours, or next onehour). After performing step 156, the system proceeds to step 158.

In step 158, a determination is made as to whether identification data(e.g., Social Security Number, frequent flier number, serial number,etc.) logged using designated antennas 52 (e.g., in the airport, or inthe gate area for the particular flight, etc.) match the identificationdata of any passengers on the reservation list for flights scheduled toleave in the next predetermined time period. If so, the system proceedsto step 160. If not, the system proceeds to step 162.

In step 160, the system checks in the qualifying passengers (thoselogged using designated antennas and matching the identification data ofpassengers on the reservation list for flights scheduled to leave in thenext predetermined time period). The system further assigns seats (thismay be based on known customer preferences, such as preferences storedfor frequent fliers), and moves the checked in passengers from thereservation list to the checked in list. This is so that there is noneed to search for passengers who have already checked in, next timestep 156 is executed. After performing step 160, the system proceeds tostep 166.

In step 162, a time delay is imposed so that the system is freed up toperform other tasks. After performing step 162, the system proceeds tostep 164.

In step 164, the time is updated. In other words, the system time isretrieved for purposes of defining the predetermined time period of step156. After performing step 164, the system proceeds to step 156.

In step 166, a time delay is imposed so that the system is freed up toperform other tasks. After performing step 166, the system proceeds tostep 168.

In step 168, the time is updated. In other words, the system time isretrieved for purposes of defining the predetermined time period of step156. After performing step 168, the system proceeds to step 156.

In one embodiment, the transponder device 32 is manufactured usingtechniques such as those described in a commonly assigned U.S. patentapplication (attorney docket MI40-048) titled “Tamper Resistant SmartCard and Method of Protecting Data In a Smart Card”, filed Feb. 13,1997, listing as inventor John R. Tuttle et al., now U.S. Pat. No.5,988,510, and incorporated herein by reference. In one embodiment, thedevice 32 includes a magnetic stripe which the carrier (e.g., airline)can use for various purposes instead of or in addition to using theantennas 42. For example, an airline may use the antennas 42 to check ina passenger, but may use the magnetic stripe with a card reader at agate 22 (such as the card reader described in U.S. Pat. No. 5,010,240)in place of a boarding card when a passenger passes through the gate 22to board a plane, or vice versa.

In one embodiment, the system gives an indication to a passenger thatthe passenger has been successfully checked in, such as by displaying amessage on a monitor, on a display on the card 32 (described elsewhereherein), by making an announcement on a speaker, or by other means.

In one embodiment, a similar method and routine is used to check inluggage bearing a card 32 (or a miniature tag housing the integratedcircuit 34) which is configured to transmit data indicating the card isassociated with checked baggage (instead of carry-on baggage or otherequipment) in response to a command from the interrogator. The luggagecan be checked in instead of or, preferably, in addition to thepassenger. This way, the passenger can just leave the luggage in adesignated area instead of waiting in a line. Airline personnel candetermine the destination by interrogating the card 32 or tag on thebaggage. Thus, the card 32 or tag becomes an electronic (recyclable)baggage tag. In one embodiment, the card 32 or tag on the checkedbaggage includes a display (as described elsewhere herein), whichdisplays the destination of the baggage (and/or transfer points).

In one embodiment of the invention (see FIGS. 1-3), the system 12communicates custom travel (e.g. flight) information to a passenger. Thesystem 12 uses the computer of the previously described carrierreservation and baggage tracking system 152. The system further includesmonitors 170 and/or speakers 172, and appropriate converters 174 and 176connecting the monitors and speakers to the network. The converters 174,for example, may convert from EGA, VGA, or super VGA to a standardtelevision signal, and the converters 176, for example, may be soundcards or equivalent circuitry. Whenever a passenger is in proximity toan antenna located near a monitor or speaker, the interrogator 50determines this in the same way that the interrogator 50 locatespassengers, by communicating with a card 32 possessed by the passenger.The system accesses the reservation and baggage tracking system 152,retrieves the departure information for that passenger, and displays theinformation on the monitor as shown in FIG. 3. More particularly, thesystem uses the existing reservation database of the system 152,including information identifying passengers who have purchased ticketsfor a flight, and information about scheduled departures. Theinformation includes existing information such as a flight, bus or trainnumber 178, destination 180, a gate, bay, or track number 182, scheduleddeparture time 184, and status information 186 (e.g., boarding, on time,delayed, gate change, see agent, cancelled, etc.).

If multiple passengers are in communications range of the antenna nearthe monitor 170, information will appear tailored for each of thesepassengers, as shown in FIG. 3. The information displayed thereforepreferably includes the passenger's name 188 (or an identifying code ornumber known by the passenger), as well. The information may be sorted(arranged) by passenger name in alphabetical order, by scheduleddeparture time, or by order of detection of the passengers by theinterrogator 50.

In one embodiment, shown in FIGS. 10 and 11, an alternative card 32B isprovided which is similar to the card 32, but further includes a display190 coupled to the integrated circuit 34. The display 190 can be aliquid crystal display, LED display, or other type of display. In thisembodiment, the customized information for the passenger bearing thecard 32B appears on the display 190. The display 190 can be activated bybringing the card 32B in communication range with a designated antenna52 in the facility (which may be arranged to have a small rangerequiring close proximity, so the display is not continuously activatedwhile the passenger travels through the facility). Alternatively, thecard 32B is further include an actuator 192 coupled to the integratedcircuit 34, actuation of which causes display of the information. Theinformation can be similar to the information displayed on the monitor170, if a monitor 170 is used, except that the name of the passenger maybe omitted because the bearer of the card 32B is obviously thepassenger. On the other hand, it may be desirable to display thepassenger name to avoid mistaken swapping of the cards 32B or to avoidtheft. The actuator 192 may be connected to an analog or digital inputpin of the integrated circuit.

In the embodiment of FIGS. 10 and 11, the card further includes a buffermemory 194 coupled to a serial input/output port of the integratedcircuit 34, a controller 196, and a display driver 198. The serial inputoutput port is used to load the buffer memory 194, and then thecontroller 196 and display driver 198 drive the display 190.

Although the system of the invention has been described in connectionwith an airport and airline reservation system, it will be apparent thatthe system also has application to other travel depots and reservationsystems, for those traveling by train, boat, bus, etc.

In one embodiment, systems of multiple facilities (airports) areconnected together, such as by using a telephone link, wide areanetwork, Internet, Intranet, etc., so that data can be shared amongvarious systems. In this embodiment, the location of checked luggage,carry-on luggage, equipment, or individuals can be determined if thelocation is within communications range of an interrogator in any of theconnected facilities (airports).

Various other applications for the system 10 will readily be apparent tothose of ordinary skill in the art.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A system for locating an object, the system comprising: an outputdevice; a plurality of databases; a plurality of interrogators, eachinterrogator electrically coupled to a plurality of antennas, each ofthe interrogators configured to communicate with radio frequencyidentification (RFID) tags within communication range of each respectiveinterrogator; and a plurality of controllers, each controllercommunicatively coupled to one or more of the interrogators and to oneor more of the databases, each controller being further configured tostore in one or more of the databases information associated with RFIDtags within communication range of each respective interrogator, each ofthe controllers being further configured to receive an object identifierassociated with the object and to access the databases to locate theobject, each controller causing the output device to output a locationof the object.
 2. The system of claim 1, wherein the output devicecomprises a display.
 3. The system of claim 2, wherein the display isincorporated on the RFID tags.
 4. The system of claim 1, wherein theplurality of interrogators is communicatively coupled to each other andeach interrogator is configured to share information with otherinterrogators.
 5. The system of claim 1, wherein the plurality ofdatabases comprises log files stored on each of the controllers.
 6. Thesystem of claim 1, wherein the object identifier comprises a uniquenumber assigned to a person.
 7. The system of claim 1, wherein theobject comprises a person.
 8. The system of claim 1, wherein the objectcomprises inventory.
 9. A system for managing objects in ageographically dispersed environment, the system comprising: a pluralityof sites, each of the sites being remotely located from other sites; aplurality of radio frequency identification (RFID) tags, each RFID tagbeing associated with an object; one or more interrogators located ateach site, each interrogator being communicatively coupled to one ormore antennas and configured to communicate with and to log a presenceof any RFID tag within communication range of the antennas; a networkcommunicatively coupling the one or more interrogators; and an accesssystem communicatively coupled to the network, the access systemconfigured to receive identifying information associated with the objectand to access a log to locate the object.
 10. The system of claim 9,wherein the log comprises a database.
 11. The system of claim 9, whereinthe log comprises a log file stored on each respective interrogator. 12.The system of claim 9, wherein each of the one or more interrogators arecommunicatively coupled to the network via a controller.
 13. The systemof claim 9, wherein each interrogator is configured to share informationwith other interrogators.
 14. The system of claim 9, wherein eachinterrogator is further configured to triangulate to determine aposition of an RFID tag when the RFID tag is detected by a plurality ofantennas.